Soil: Sand is composed largely of silica,
therefore, the
roots of soil grown plants are immersed in a potential "silica reservoir".
Although this form of silica is very insoluble it does dissolve
slowly - especially with alkaline waters.

However, plants grown in hydroponic systems
without soluble silica supplements, typically contain much less silica in
their cells. This occurs because, unlike soil grown plants, silica is
virtually absent at the root-zone:

Recycling
systems: Once the plant
consumes the silica present in the make-up water, no
more silica is available. Of course if either rainwater or RO
(reverse osmosis) water is used, no soluble silica is present.

Research shows that the
absence of silica in hydroponics can cause plant health to be less than
optimum.

*Note, silica cannot be included in concentrated
nutrient formulations because stable silica solutions are by nature highly
alkaline. It must therefore be added separately.

When to use Silica?

Silica should be used from seed to harvest: To benefit new growth,
silica must be present at all times in the nutrient solution. Electron
microscopy and x-ray analysis both confirm that once silica is deposited,
it can no longer be redistributed within the plant.